The most commonly used metals in surgery are surgical stainless steel and titanium. Surgical stainless steel is a term used to label particular grades of stainless steel that are commonly used in biomedical appliances. The most common forms are austenitic 316 stainless steel and martensitic 440 and 420 stainless steels and whilst there is no certain definition of what constitutes surgical stainless steel, manufacturers generally recognise this to be any grade of corrosion resistant steel.
316 stainless steel is an alloy of chromium, nickel and molybdenum that is highly resistance to corrosion and relatively strong. 316 stainless steel can be cheaper to produce than the commonly used titanium alloy, Ti6AI4V, and as such is commonly used in the production of biomedical implants. Its drawback, however, is the nickel content which can induce a reaction with the immune system and cause complications. For any implants which may be subject to pressure once in place, such as body piercings, bone fixation screws and prostheses, austenitic steel is more commonly used.
Titanium has been commonly used for biomedical purposes since the 1950s, after already having been used in dentistry prior to this. It is commonly used to make prosthetics and can be used as the material for biomedical implants all over the body from false eye implants and spinal fusion cages, to pacemakers and hip replacements. In addition to thus, several surgical instruments are coated with titanium nitrade, an extremely hard ceramic material that hardens and protects surfaces. Titanium is commonly considered to be the most biocompatible metal due to its high level of corrosion resistance and high fatigue limit. A protective oxide film forms naturally in the presence of oxygen, which protects it from bodily fluids and prevents reactions between the metal and hosting environment.
Although both materials are useful, there are several differences between them that make them suitable for different things. Titanium is stronger and more lightweight than stainless steel, and less rigid which can limit the amount of stress placed on bones. It also lasts longer and generally has superior strength to stainless steel, although stainless steel is still commonly used in implants which will be placed under heavy strain. Another plus point for titanium is the fact that it does not contain nickel, making it by far the better option for those with proven or suspected nickel allergies. It is estimated that 10-20 percent of the population is allergic to nickel, which is a massive figure, and it is one of the main causes of contact dermatitis.